In all leagues that I've seen, owners waive most of their young players immediately after the trade deadline. My impression is that in doing so, and if the players are not claimed, that it continues eligibility without using up option years.

I'm not sure what exactly you're asking but most do it for roster flexibility. Most are put on revocable waivers.
1. Any player who clears waivers can be traded after the trade deadline.
2. Any player who clears waivers can be demoted.